1. Field of the Invention
This invention relates to a process for producing a semiconductor member and a process for producing a solar cell. More specifically, this invention relates to a process for producing a semiconductor member and a process for producing a solar cell which processes have the step of transferring a semiconductor layer to the part of a second member by making separation in the part of a porous layer.
2. Related Background Art
Studies are widely made on solar cells as a drive energy source of various appliances and a power source for connecting commercial electric power systematically. It is desired for the solar cells that their devices can be formed on inexpensive members because of requirements on cost. However, expensive single-crystal silicon members (wafers) are commonly used as semiconductors which constitute the solar cells.
As a method for making solar cells low-cost, for example Japanese Patent Applications Laid-open No. 7-302889 and No. 10-135500 disclose a method in which a peeled thin-film single-crystal semiconductor layer is used.
According to these publications, a solar cell is conventionally produced in the following way. First a p+-type surface layer is formed at the surface of a single-crystal silicon member 101 (corresponding to 101 in FIG. 1A) and the p+-type surface layer is subjected to anodizing to form a porous layer. Next, a semiconductor layer is formed on the porous layer. Subsequently, for example, a support member on which an adhesive layer has been formed is bonded to the semiconductor layer. Then, the porous layer is broken (i.e., the bonded structure obtained is separated at the porous layer) to transfer the semiconductor layer to the support member side. Then, electrodes and so forth are formed on the support member side to which the semiconductor layer has been transferred.
In such a conventional method, however, the porous layer is formed over the whole surface of the single-crystal silicon member 101, and hence, where the porous layer formed has a low strength, the porous layer itself may unwantedly break before the separation for transferring the semiconductor layer to the support member side. Accordingly, when the porous layer is formed, it has been required to set anodizing conditions strictly so as to prevent such break.
Accordingly, an object of the present invention is to make the semiconductor layer unseparable from the single-crystal silicon member before the separation for transferring the semiconductor layer to the support member side, without setting the anodizing conditions strictly.
To achieve the above object, the present invention provides a process for producing a semiconductor member, comprising:
a first step of forming a porous layer by making porous a first member prepared or an epitaxial layer formed at the surface of the first member, leaving some region or regions thereof not made porous;
a second step of bonding a semiconductor layer formed on the porous layer and on the first member or epitaxial layer that is left not made porous, to a second member to form a bonded structure; and
a third step of separating the bonded structure in the part of the porous layer, at the interface between the porous layer and the first member or at the interface between the porous layer and the semiconductor layer to transfer the semiconductor layer to the second member side,
wherein the first member or epitaxial layer is made porous leaving some region or regions thereof not made porous so that the porous layer does not cause any separation in the part of the porous layer, at the interface between the porous layer and the first member or at the interface between the porous layer and the semiconductor layer in the first and second steps.
The present invention also provides a process for producing a solar cell, the process comprising the steps of producing a semiconductor member by the above semiconductor member production process, and providing the semiconductor member with an electrode.